Flexible geiger counter



12, 1963 H. a. RICHTER ETAL 3,110,335

FLEXIBLE GEIGER COUNTER Filed Dec. 6. 1961 INVENTORS.

Harold G. Richfer y Arfhur S. Gillespie, Jr.

ATTORNEY.

United States Patent 3,116,835 FLEXHBLE GEE-GER CGUNTER Harold G. Richter, Chapel Hill, and Arthur El. Gillespie, Ira, Durham County, N.C., assignors to the United States of America as represented by the United States Atomic Energy Commission Filed Dec. 6, 1961, Ser. No. 157,668 6 Claims. (Cl. 313-93) This invention relates to a flexible Geiger counter that has stable plateau characteristics whether the counter is coiled or straight and that may be capable of counting pulses in excess of 300,000 counts per minute, depending upon the length of the counter, with little coincidence loss.

Conventional prior art straight tube Geiger counters are rigid and could not be coiled or placed in a variety of configurations. For some uses for Geiger counters, such as Wraparound-pipe or other uses where a coiled configuration is desired, the rigid straight tube counter obviously could not be used for these purposes.

With a knowledge of the limitations of prior counters in regard to their rigid construction, it is a primary object of this invention to provide a flexible Geiger counter which can be coiled or placed in a variety of selected configurations while at the same time function efliciently as a Geiger counter.

It is another object of this invention to provide a flexible Geiger counter that is easily fabricated and assembled.

It is still another object of this invention to provide a flexible Geiger counter which is capable of counting pulses in excess of 300,000 counts per minute with little coincidence loss.

These and other objects and advantages of this invention will become apparent upon a consideration of the following detailed specifications and the accompanying drawing, wherein:

FIG. 1 is a sectional View of a flexible Geiger counter which is made up from a plurality of short segments of corrugated plastic material;

FIG. 2. is a view of a flexible Geiger counter utilizing a plastic vacuum cleaner hose; and

FIG. 3 is a View of a cage-like assembly for supporting an anode wire electrode for use in and as a part of the counter of FIG. 2.

The above objects have been accomplished in the present invention by constructing the flexible Geiger counter from materials composed of vinyl chloride polymerized with plasticizers or co-polymers. The counters can be made either by adding short segments of corrugated plastic sleeving together, or by starting with a length of vacuum cleaner hose. The anode can be maintained axial Within the sleeving or hose during tube flexing by means of polystyrene spacer disks or an easily assembled polyethylene flexible cage. The cathode is a wire spiraled on the outside of the counter. The sleeving or hose is fitted with glass end-pieces or any other good insulator to maintain the anode Wire taut and to admit a counting gas mixture into the counter. When a counting gas was flowed through the counter, the result was found to be a satisfactory Geiger-Muller counter.

In the drawing, FIG. 1 illustrates one embodiment of a flexible counter in which the principles of this invention may be carried out. The counter of FIG. 1 is made with a plurality of short segments 4 of corrugated plastic material. These segments 4 are from 2 to 3 inches long, for example, and are formed in the following manner. Plastic sleeving such as PVC-744, for example, is slipped over a threaded rod mandrel of diameter slightly less than that of the sleeving. Wire is Wrapped around the Patented Nov. 12, 1963 lice plastic, in the threads of the rod, and kept taut while the assemblage is heated at 110 C. for 20-30 minutes. After cooling, the plastic tubing is removed from the threaded mandrel, whereupon it maintains a corrugated tubular shape. The ends of the mandrel are of slightly different diameters, such that the larger end of one formed segment can be slipped loosely over the smaller end of another segment.

A polystyrene disk 3, 0.5 cm. thick by 2.3 cm. diameter, containing a 25-mil central hole and three peripheral holes to permit passage of gas, is fastened with adhesive in the smaller end of each of the segments 4. Any desired length of flexible counter can thus be built up by threading the required number of segments 4- on a molybdenum or tungsten anode wire 1, the anode lwire ll passing through the central hole in the disks 3, and gluing the seams of the segments 4- where they overlap. A bare copper wire 2 is spiraled in the grooves on the outside of the assembled counter and serves as the cathode of the counter.

End pieces 5 and 6 are glass T-tubes or any other good insulator and are attached to the counter tube by means of rubber stoppers 2.4 and 214i, respectively. Any other suitable means may be used for attaching the end pieces to the counter tube, if desired. The anode wire 1 is slipped through split rubber stoppers 7 and 8, for example, in the end of glass tubes 5 and 6 which permits the anode wire to be tightened or loosened as the occasion requires. It should be understood that any other suitable means may be used for releasable holding the anode wire taut.

The anode wire 1 is connected by a lead 9 to the positive terminal of a power supply Ill, which may be a battery, for example, while the negative terminal of power supply 10 is connected by a lead 11 to the cathode wire 2. A battery is but one convenient means for supplying operating voltage to the counter. For example, a blocking oscillator, step-up transformer rectifier and filter circuit, with means for regulating the output voltage may be used in place of a battery.

A source 17 of counting gas which may be Q-gas (98.7 percent helium, 1.3 percent butane), for example, is connected by means of tubing 16, valve 15, tubing 14 and portion 12 of the tube 5 to the interior of the counter. This gas flows through the counter, through portion 13 of tube 6, tubing 18, and is exhausted thereby.

The signals received by the anode wire 1, which serves as a collector electrode, are fed by a lead 20 to an amplifier 21. Amplifier 21 is connected by a lead 22 to a counter circuit 23 which includes a sealer, count rate meter, and recorder.

The plastic tubing used to make the short segments 4 of the counter of FIG. 1 may be any one of several commerioally available tubings. Examples of tubing suitable for the counter are SLY-105, Tygon R3603, PVC-744, PVCAOS, and Dacron-Tygon. The Dacron-Tygon tubing is a knitted Dacron (methyl terephthalate-ethylene glycol polyester fiber, Dupont Company) cloth tubing made gas tight with Tygon paint containing colloidal graphite. The SLY- tubing is made by 'Illurnitronic Engineering, Sunnyvale, California. Tygon R3603 is made by the US. Stoneware Company, Tallnradge, Ohio. PVC-105 and PVC-744 are made by the Alpha Wire Corporation, New York, New York. All of the above mentioned tubings are composed of vinyl chloride polymerized with plasti cizers or co-polymers and their exact chemical compositions are proprietary items of manufacture by their respectiveproducers. Their respective designations are trade names and the various tubings are commercially available. It should be noted that the counter is not limited to these materials since any other material which is sufficiently conductive for conducting the minute cur- '3 rents making up the Geiger pulse may be used in the counter.

The disks 3 may be made from either Teflon, polystyrene, Lucite, or polyethylene, or any other suitable plastic material. All of these materials have been individually used and found suitable as spacer disks for the device of FIG. 1. The anode wire 1 can be made from 2, 3, 5 or mil tungsten or molybdenum wire, for example. A 5, 10' or mil copper wire can also be used for the anode. In fact, most any metal Wire may be used for the anode.

The counter of FIG. 1 may be made any selected length dope ding upon the number of the short segments used in assembling the counter. For example, it may be a few inches long or it may be as long as ten feet or greater, if desired. When PVC-744 tubing with a diameter of 3 cm. is used in the counter of FIG. 1, the smallest radius of curvature possible with the assembled counter is about 3 cm.

Counting characteristics of the flexible counter of FIG. 1 are essentially independent of the configuration of the tube; i.e., good plateaus can be obtained whether the counter is straight or coiled. Various anode materials and diameters have been used in the counter of FIG. 1 and little difference in operating characteristics have been observed. The choice of anode is determined by convenience.

The device of FIG. 1 is not limited to the use of a plurality of short segments to malze up the counter. For example, where the length of the counter desired is not greater than the heat-treating oven used in forming the corrugated tubing, the mandrel and the plastic sleeving may be made as long as can be permitted by the dimensions of the oven. Thus, a unitary corrugated plastic tube may be formed and heat-treated in the oven, and the counter would then be a unitary device and would not be formed by a plurality of short se ments glued together. With such a unitary plastic tubing, the anode wire would have the plastic disks fastened thereto at intervals with adhesive and the wire and disks would then be carefully slipped into the corrugated tubin The device of FIG. 1 is shown straight for the sake of clarity. It should be understood that it be coiled one or more times or be placed in several different configurations as desired or required. Good plateaus are obtained whether the counter is straight or coiled.

Another technique for making flexible counters is by using plastic vacuum cleaner hose. Examples of vacuum cleaner hose that can be used in Geiger counters are Nylafiex, Dayflex, and Vac-U-Flex. These hoses have an inside diameter of 1.25 inches and are from 6 to 10 feet long. They are polyvinyl chloride formulations, with the Nylaflex having, in addition, a reinforcing layer of nylon braid.

FIG. 2 is a view showing a flexible counter utilizing a vacuum cleaner hose. The hose is provided with a ":-tube '26 madeof glass or any other suitable insulator which is held in one end of the hose with an insulator stopper which may be rubber, for example. Tube 26 is provided with a portion 27 for admitting a counting gas to the counter. The end of tube as is provided with a split rubber stopper 3%, for example, for holding an anode wire 25* wh'ch extends through hose 25 and which is held substantially axial within hose 2 5 by means of spacer dislrs in a manner to be described below. it should be understood that means other than the split rubber stopper may be used for releasably holding the anode wire.

The other end of hose 25 is provided with a T-tube 31 made of glass or any other suitable insulator. Tube 31 is provided with a portion 32 for exhausting the counting gas from the counter. The tube 31 is held in the other end of hose 25 by means of an insulator stopper. The end of tube Ill is provided with a split rubber stopper 33 or equivalent means for holding the other end of anode i wire 29. A wire 23 which is wound around the outside of hose 25 serves as the cathode when Nylailex or Dayilex hose is used in the counter. When a Vac-U-Flex hose is used in the counter the heavy spiraled wire already built in can be used as the cathode, if desired, or an external wire may be used if preferred.

The anode wire 29 which serves as the collector electrode for the counter is supported axially within hose 25 by means of a polyethylene spacer assembly as shown in FIG. 3. Polyethylene disks 35 are 1% inches in diameter. Four A-ineh holes for gas passage are bored near the perimeter of each disk, and four -inch holes are spaced equally between the larger holes, as shown in FIG. 3. A. ZS-mil hole in the center of each disk 35 carries the anode wire 29. A pair of polyethylene strips as, notched at each end, are inserted in the smaller holes in the disks and serve to keep the disks separated at a selected distance from 2 to 3 inches, for example, depending upon the lengths of the strips. The above specific material and dimensions are given by way of example only. It should be understood that they may be changed or modified, as desired or required, to be used within any size flexible tubing that may be used in constructing the counter. The flexible cage-like assembly of FIG. 3 can then be inserted into the hose 25 of PEG. 2 and the anode wire 25 drawn taut through the members 369 and 33. it should be noted that springs may also be used for keeping the anode wire taut. The assembly of PEG. 3 is drawn larger than it actually is for the sake of clarity.

A source of operating potential, not shown, is connected between the anode wire 29 and cathode wire 23 in the same manner as is done in PEG. 1. During operation of the device of FIG. 2, a counting gas is flowed through the counter and the signal output from the counter is collected by anode wire l and fed to an amplitier and pulse counter in the same manner as in the device of PK}. 1.

The flexible cage-like assembly of FIG. 3 may be used in the counter of FIG. 1 if desired, or in corrugated plastic tubing other than vacuum cleaner hose when such tubing is used in constructing the counter.

Pules heights of flexible Geiger counters such as illustrated in MG. 1 and FIG. 2 are smaller than those of conventional metal-cathode tubes. Best results can be obtained with the devices of FIG. 1 and FIG. 2 by using a 50-millivolt sensitivity setting on the sealer in the counting circuit 23 of HG. l.

Plateaus obtained with the above-described flexible counters are exceptionally long and very fiat, whether the counters are coiled or straight. A segmented counter of PVC-744 shows a SOO-volt plateau (Q-gas) with a 5 percent per volts slope. A ten-foot Vac-U-Flcx counter containing the polyethylene cage anode assembly shows less than a 2 percent per 100 volts slope over almost 1000 volts.

The long plateaus obtainable with the above flexible counters apparently result directly from the semiconducting property of the plastic tubing. The Wall material produces a situation which acts as if there were a parallel resistance-capacitance network between the place where positive ions are collected and electrical ground. The high voltage applied between anode and cathode is therefore distributed partly between anode-and-wall and wail-and-cathode The actual electrical field which an electron just formed in the counting gas experiences is thus less than that indicated by the measured potential between anode and cathode. Another reason for the long plateau is that production of secondary electrons by positive ions at the plastic wall is much lower than with metal cathodes, partly because no conduction electrons are available for multiple emission processes, and partly because the work function of the plastic surface is high. When the counters are coiled such that there is not perfect symmetry between the anode and cathode, the above properties of the plastic tubing will insure long plateaus for the counters even with this slight asymmetry between the anode and cathode.

Counting rates for the above counters are very high, in excess 300,000 counts per minute for long counters, because of their segmented construction. Geiger pulses are not propagated beyond insulating obstructions placed on the anode. Each of these counters, with its polystyrene or polyethylene spacers, is a series of short, independent G-M counters, any one of which can operate irrespective of the recovery of its neighbors. Long flexible counters made up of many segments will thus only be limited in counting rate by the resolving time of individual segments or sealer circuitry.

In some prior art Geiger counters, a phenomenon known as the sheath eliect will sometimes drastically reduce the pulse heights obtained by these prior counters. In these prior counters, as the counting rate is increased by bringing a distant radioactive source up close, it is possible with an oscilloscope to watch the discharge pulse heights decrease markedly in size. This is caused by the sheath effect. Electrostatic charge collects on the interior wall of the counter from the Geiger discharges and is only slowly drained off to the exterior cathode. If suthciently high radioactivity decay rates are encountered, this charge can build up to such values than an ion pair just created in the counter gas sees a reduced potential on the anode. The resulting smaller output pulses may not trigger the scaler. However, with the PVC-744 counter and vacuum cleaner hose counter of this invention, counting rates up to 100,000 counts per minute have been observed on a single segment and the pulse heights were still above 50 millivolts. Thus, there is only a very minor sheath eflect in the counters of this invention, be cause of the plastic construction of the counters.

In a typical test, a Nylaflex flexible counter was put into operation with Q-gas, and after more than 50 hours continuous operation and more than 3X10 counts regisered, no deterioration in count rate, plateau, or pulse height could be detected. Thus, it can be seen that the counters of this invention have substantially stable operating characteristics over long periods of time. It can be inferred that the decomposition products from Geiger discharges in Q-gas do not cause these flexible counters to deteriorate in performance. These flexible counters can be used as anti-coincidence coils, large volume liquid dip-counters, wrap-around-pipe counters, etc.

This invention has been described by Way of illustration rather than limitation and it should be apparent that this invention is equally applicable in fields other than those described.

What is claimed is:

1. A flexible Geiger counter adapted to be placed in several non-linear configurations while at the same time producing no substantial deterioration in count rate, plateau, and pulse height over long periods of operation, comprising a corrugated conductive, polyvinyl chloride tubing, an anode wire disposed within said tubing for collecting the output pulses of said counter, a plurality of plastic spacer disks threaded on said anode wire for holding said wire substantially axial within said tubing, said disks being provided with a plurality of apertures for allowing a counting gas to flow through said tubing, a cathode wire disposed around the exterior of said tubing in the corrugations thereof, insulator T-tube end pieces fitted within the ends of said tubing, one of said tubes serving as a means for admitting said counting gas to said tubing, the other of said tubes serving as a means for exhausting said gas from said tubing, a stopper fitted within the end of each of said glass tubes, said anode wire extending through said stoppers and adapted to be held taut within said tubing by said stoppers, a source of operating voltage for said counter, said anode wire and cathode wire being connected across said voltage source, a pulse rate counting circuit, and means for conmeeting said anode wire to said counting circuit.

2. The flexible counter set forth in claim 1, wherein said tubing is made up of a plurality of short, overlapping corrugated segments glued together, and said spacer disks are spaced apart about 2.5 inches.

3. The flexible counter set forth in claim 1, wherein said counting gas is Q-gas, consisting of 98.7 percent helium and 1.3 percent butane.

4. The flexible counter set forth in claim 1, wherein said tubing is a vacuum cleaner hose.

5. The flexible counter set forth in claim 4, wherein said spacer disks are spaced apart about 2.5 inches, and a pair of plastic strips being disposed between each pair of disks and affixed thereto to form a cage-like assembly for supporting said anode wire within said hose.

6. The flexible counter set forth in claim 5, wherein said hose is Nylaflex, and said disks and strips are polyethylene.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A FLEXIBLE GEIGER COUNTER ADAPTED TOBE PLACED IN SEVERAL NON-LINEAR CONFIGURATIONS WHILEAT THE SAME TIME PRODUCING NO SUBSTANTIAL DETERIORATION IN COUNT RATE, PATEAU, AND PULSE HEIGHT OVER LONG PERIODS OF OPRATION, COMPRISING A CORRUGATED CONDUCTIVE, POLYVINYL CHLORIDE TUBING, AN ANODE WIRE DISPOSED WITHIN SAID TUBING FOR COLLECTING THE OUTPUT PULSES OF SAID COUNTER, A PLURALITY OF PLASTIC PAPER SPACER DISKS THREADED ON SAID ANODE WIRE FOR HOLDING SAID WIRE SUBSTANTIALLY AXIAL WITHIN SAID TUBING, SAID DISKS BEING PROVIDED WITH A PLURALITY OF APERTURES FOR ALLOWING A COUNTING GAS TO FLOW THROUGH SAID TUBING, A CATHODE WIRE DISPOSED AROUND THE EXTERIOR OF SAID TUBING IN THE CORRUGATIONS THEREOF, INSULATOR T-TUBE END PIECES FITTED WITHIN THE ENDS OF SAID TUBING, ONE OF SAID 